There are cases in which a failure occurs owing to there being duplicate IP addresses in the same subnet. That is, in the same subnet, if the same IP address is assigned to different host computers, there is a possibility that a failure will occur, which is problematic.
In the same subnet, if the same IP address is assigned to different hosts, more specifically, a problem will occur in cases such as those described below. In a case where a device outside a subnet transmits a packet in which a duplicate IP address is used as a transmission destination, a router of the subnet refers to an address resolution protocol (ARP) table and transfers the packet. However, there is only one pair of an IP address and a MAC address, which are written in the ARP table. For this reason, even in a case where an IP address is assigned in a duplicated manner to different hosts, the packet is transferred to only the host computer having a MAC address written in the ARP table, and the packet is not transferred to the other host computers.
The ARP table in the router is updated moment by moment in accordance with the communication situation, such as being updated when a packet is transmitted finally in the router. For this reason, if an IP address has been assigned to different host computers in a duplicated manner, the packet arrives at only wrong host computers, with the result that the communication is disconnected or an interruption occurs.
Therefore, a technology for detecting duplication of IP addresses in the same subnet is an important technology in managing and supporting a network system. Typical methods for detecting such a duplication of IP addresses are the following. In one method, ARP request packets are transmitted by broadcasting by using an IP address in a subnet as a destination, and a response to the ARP request packet is checked. When the IP address has been duplicated, an ARP response is returned from a plurality of host computers. Consequently, it is possible to find the duplications of the IP address.
However, in the method, an ARP request packet needs to be transmitted to all the IP addresses in the subnet for which it is desired to find duplication of IP addresses. Therefore, the method has a problem in that scaling is not easy and the cost is high.
The following documents are examples of disclosing techniques for detecting duplication of IP addresses.
Japanese Laid-Open Patent Publication No. 09-321757.
Japanese Laid-Open Patent Publication No. 07-038597.
Japanese Laid-Open Patent Publication No. 03-212038.